Lymphangiomatosis is a rare disorder. It is commonly localised in the skeletal system and called Gorham’s disease, and in thoracic or abdominal organs. Involvement of the pericardium is rare and has been described in less than 20 patients worldwide. The case of a 14-year-old boy presenting with asymptomatic chylopericardium and interstitial lung disease is presented. After lung biopsy, performed to confirm the diagnosis of pulmonary lymphangiomatosis, he developed chylothorax and massive loss of chyle via chest drains. Thoracic duct ligation did not result in clinical improvement. Treatment with interferon α2b was given and because of clinical deterioration radiotherapy was added to the treatment. This resulted in a rapid decrease of chyle production in the patient.